The bulk of the research proposed in this application will deal with the kinetics of mating in Drosophila. Prime variables for each tested strain or species will be (1) time allowed for mating, (2) the volume of the mating chamber, and (3) the numbers of males and females within the chamber. The generality of the results will be ascertained by studying at least two wild strains of D. melanogaster as well as ebony and sepia strains (preliminary data on sepia are available); D. pseudoobscura, D. persimilis, and D. simulans will also be tested. These studies are intended to reveal the general, relatively simple aspects of mating kinetics in Drosophila which can be observed despite the known complexities of the courtships and other reproductive behaviors of these flies. Knowledge of the mating kinetics of single species should aid in the interpretation of observed sibling-species responses to simulated sterile-male control efforts (a separate research project). A second, special effort (to be undertaken in collaboration with Dr. Stella Crossley, a visiting professor from Monash University, Australia) will involve the mating kinetics of geographic strains of D. melanogaster (Riverside, California; Bermuda; Madeira) where it is known that the receptiveness of females and the courting aggressiveness of males differ considerably. Such strains (say, A and B) will be studied in all combinations; A x A, A x B, B x A, and B x B. The results should bear on the notion that asymmetries in the mating behaviors of the two sexes are important in the origin of the sexual isolation of newly arisen species.